New Report Finds Dams Threaten Fish Diversity

GLOBAL - Without more careful planning, species extinctions and basin-wide declines in fisheries will accompany new hydropower development in the worlds major tropical rivers says a report published in Science Magazine co-authored by WorldFish, Senior Scientist, Eric Baran.

Around 837 dams already exist in the Amazon, Congo, and Mekong rivers, and over 450 additional dams are planned. Together, these three rivers are home to roughly one third of the world’s fresh water fish and many unique fish species. Fish are a vital source of nutrition and livelihoods for the millions that live near the rivers.

In the Lower Mekong basin alone, freshwater capture fisheries provide up to 80% of the animal protein consumed by those who live there.

Dams are usually built where rapids and waterfalls boost hydropower potential. Unfortunately, these areas are also home to high fish biodiversity. Large dams reduce fish diversity but also block fish migration that connects populations and enables species to complete their life cycles.

Dams can reduce fish access to floodplain habitats that are essential nursery areas and feeding grounds. Model simulations of proposed dams in the lower Mekong Basin predict major reductions of migratory stocks.

Eric Baran, Senior Scientist, WorldFish: “In tropical countries, the impact of dams on biodiversity and fisheries has been seriously overlooked. Funders are not being given the full picture when it comes to assessing dam proposals, and dam development is not planned and coordinated at the relevant scale. In the Mekong for instance, there is currently no planning process beyond the national level, although most dams have an environmental and social impact at the regional scale.”

The report’s authors call for a more sophisticated and holistic planning process that takes into account the cumulative effects of dams planned for the future.

They highlight increased spatial data availability that can be used to support better analysis of the trade off between hydropower potential and the sustainability of key natural resources. It is also possible to build on new spatial analysis tools in which the cumulative benefit, in terms of hydropower production, of a combination of dams is weighted against their cumulative impact on fish biodiversity and production.